1. Field of the Invention
The present invention relates to an electronic circuit and an electronic device using the electronic circuit and, for example, relates to a mobile terminal such as a mobile phone.
2. Description of the Related Art
Conventionally, a plurality of IC chips (chipset) are incorporated in an electronic device such as a mobile terminal. An operating clock is supplied to the chipset. A high-speed clock is supplied to a circuit requiring high-speed operation, and a low-speed clock is supplied to other different circuits. In the case where a further high-speed operation is required, a clock obtained by multiplying the frequency of a high-speed clock is used, in some cases.
Further, there is available a technique that changes a supply voltage in accordance with the clock frequency. For example, a battery-powered integrated circuit to which the above technique has been applied is described in Jpn. Pat. Appln. Laid-Open Publication No. 5-119876. This example selects a supply voltage according to a selection signal output from a processing circuit. When the frequency of an operating clock signal is high, a high supply voltage which is formed by serially connecting two batteries is selected; whereas the frequency of an operating clock signal is low, a low supply voltage which is formed by connecting two batteries in parallel is selected.
Further, an image processor to which the above technique has been applied is described in Jpn. Pat. Appln. Laid-Open Publication No. 2001-238190. This image processor controls a clock signal and a supply voltage to be supplied to a processing circuit in accordance with an operation mode. More specifically, under the control of a CPU in the image processor, the image processor loads image data at a resolution and frame rate specified in accordance with an operation mode, determines the minimum supply voltage and frequency of a clock signal at which the processor can function for each set mode, and controls the clock signal frequency and supply voltage value output from a clock generator and regulator.
However, there is still room for further improvement in order to reduce power consumption.